1. Field of the Invention
The present invention generally relates to a camera apparatus, and particularly relates to a digital camera which attends to different image processing, depending on different importance of image areas.
2. Discussion of the Background
Conventionally used cameras are mostly analog cameras that expose films to light. Data photographed by such analog cameras are generally referred to as “photographs”. In the art of analog cameras, various schemes have been presented to attend to automatic control of camera functions such as focus adjustment and exposure correction, which are often difficult to users who are not familiar with cameras. Such automatic control is performed, for example, by providing a function to detect a direction of sight to identify an area of the finder that the user is looking at, and by focusing at the point of fixation.
Japanese Patent Laid-open Application No. 6-138377 discloses an analog camera, which automatically adjusts focus by use of a sight detection means for detecting a fixation point of the user eye and a focus detection means for detecting focus points at a plurality of positions. Japanese Patent Laid-open Application No. 8-46833 discloses an analog camera which attends to automatic focus control and automatic exposure control by use of a sight detection means for detecting the fixation point of the user eye.
Cameras that are generally referred to as a digital still camera (hereinafter, “digital camera”) convert optical image data acquired through a solid camera device such as a CCD into electrical image data, and store the image data in memory such as a memory card after proper image processing and image compression.
Data acquired by a digital camera is referred to as an image since it is represented by electrical signals. With recent development of digital medium and the Internet, there has been an increasing demand for digital cameras. Different from analog cameras, digital cameras allows photographed images to be immediately checked, which provides an opportunity to take another picture in case of failure, and, also, does not require development of films. Such features explain part of the reasons why a market for digital cameras has been expanding. For example, there are increasing numbers of users who use digital cameras instead of memo notes when they attend business shows.
In the digital cameras, process steps that correspond to film development of analog cameras may include 1) image processing and 2) image compression. At the image processing step 1), color correction is necessary, for example, if a single plate camera device of a general type having only one color per pixel is used. Further, various image processing will be performed to improve image quality by attending to aperture processing (i.e., edge enhancement or sharpness enhancement), exposure correction, etc.
Even when analog cameras are used, correction to some extent may be made at the time of film development. Sharpness of the photograph and condition of exposure are almost uniquely determined by graininess of the film (i.e., film sensitivity) and focusing at the time of taking pictures.
Digital cameras, on the other hand, can perform image processing properly, thereby producing an image having better image quality than an original image obtained at the time of taking pictures. Further, image processing can improve sharpness as well as attend to binary processing, which facilitates use of digital cameras for taking pictures of texts while analog cameras are rarely used for such purpose.
Image processing is vital in digital cameras as described above, and numbers of patent applications have been filed in the art of image processing. Japanese Patent Laid-open Application No. 11-110551 discloses a color discriminating device, which is used to eliminate black area noise caused by a failure to determine colors during color correction process in the digital cameras. If the area of application is not restricted to digital cameras, there are numerous numbers of image processing schemes in the art of image processing of digital images, and these schemes are generally applicable to digital cameras. For example, Japanese Patent Laid-open Application No. 10-191064 discloses an image filtering method and apparatus that can enhance sharpness and remove noise at the same time by applying filtering with weight factors that reflect the magnitude of contrast in the vertical and horizontal directions around a pixel of interest.
In conventional schemes in the image processing of digital cameras, processing is generally applied across the board to the entire image. In some schemes, however, images are divided for processing for the image compression processing 2) that is performed prior to storage of image data in memory such as a memory card.
Japanese Patent Laid-open Application No. 10-229544, for example, assumes a direct connection of a digital camera and a printer. Since the size of memory medium provided in the digital camera is limited, the image processing apparatus disclosed in this document divides an image prior to compression, rather than compresses/decompresses the entirety of processed data at once.
Further, various image processing apparatuses that takes advantage of the fact that image data is acquired by a camera are also known to date.
Japanese Patent Laid-open Application No. 9-326025, for example, discloses an image processing apparatus which retrieves only the image data of an object located at a particular distance by storing range data that is indicative of distance between the camera and objects. In this scheme, each portion of the acquired image can be extracted according to an indication of distance, thereby making it possible to take into account intention of the camera user subsequently at the time of editing.
This scheme, however, requires a memory area for storing range data. In the worst case, a memory space is necessary that stores range data for each pixel of the image. A typical digital camera at present has 1.5 million pixels, and the number of pixels will continue to increase in the future. This scheme is thus not realistic.
Moreover, neither Japanese Patent Laid-open Application No. 10-229544 nor Japanese Patent Laid-open Application No. 9-326025 takes advantage of the fact that image data to be processed is acquired by use of a camera.
Image data that is acquired by use of a camera should be treated in accordance with its nature. If general image processing is applied without any regard to this fact, processing time becomes increasingly lengthy as processing becomes increasingly sophisticated in order to improve image quality.
Ideally, image quality should be as high as possible across the entire image regardless of greater or smaller importance of different image portions. If the highest image quality is to be maintained for the entire image, however, processing time becomes lengthy. This is the reason why a user using a digital camera often misses a chance to take a picture at an important moment because of a shutter lag, which is a time period from a moment at which a shutter button is pressed first to a moment at which the shutter button can be pressed again, and is also referred to as a photographing interval. If the shutter lag is designed to be shorter to enhance the performance that is expected of a camera, processing time set aside for image processing, image compression, and image storing needs to be shortened.
As described above, conventional digital still cameras have drawbacks in that the user is likely to miss a shutter chance because of a lengthy processing time if sophisticated processing steps are used in the image processing to improve image quality.
In the art of analog cameras, on the other hand, there is a known scheme that uses a function to detect a direction of user sight for the purpose of controlling focus and exposure. In analog cameras, however, such function to detect a direction of user sight has only been used for controlling of focus and exposure, and is devoid of any concept that suggests use of such function for improving image quality. When the drawbacks of digital cameras regarding the lengthy image processing time is taken into consideration, use of a function to detect a direction of user sight in digital cameras will make it possible to identify areas of importance in the acquired image in the manner that reflects intension of the camera user.